Method of producing a separating suspension



Nov. 9, 1954 M. g. DRIESSEN ETAL 2,693,878

METHOD OF PRODUCING A SEPARATING sus zusxon Filed Oct. 30, 1951 00 I B H and Wafer l4 Y Fl6.2

Coarse Particles Fine 5 o Particles ne FIGJ m Flofaf'on 2s Apparatus 24 w a Slime and Taillngs lizafcy 45 26 TVI'asfe Fines) :c ener Flow Divider To Fine Light 30 W0 Wafer Parficlesu s i 29 I3 Caarse Coal Hydrocyclone 46 Separator 2? Y 36 33 34 C 23 Waste Sink and Floaf Bafh ME 40; as: L To Waste INVENTORS 4T 48 Freevrk J. Fbntem Mnimlhan G. Dr'fess n, clcceuecl 5y Anije .Dnesaen, Aomlmefroiov.

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ATTORNEYS United States Patent METHOD OF PRODUCING A SEPARATING SUSPENSION Maximiliaan G. Driessen, deceased, late of Pittsburgh, Pa., by Antje G. Driessen, administrator, Amsterdam, Netherlands, and Freerk J. Fontein, Heerlen, Netherlands, assignors to Stamicarbon N. V., Heerlen, Netherands Application October 30, 1951, Serial No. 253,802

2 Claims. (Cl. 209-1725) The present invention relates to methods of producing a separating suspension. The application is a continuation-in-part of the application of Maximiliaan G. Driessen and Freerk J. Fontein filed April 23, 1946, Serial No. 664,322 for Methods of Producing a Separating Suspension, and now abandoned.

Many separating procedures utilize suspensions having a specific gravity between certain limits. For example, in the sink-and-fioat treatment used during the washing of coal, a suspension bath is provided having a specific gravity between that of the coal and that of the slate or rock. Many different kinds of particles are used for such suspensions, for example, loess, magnetite, and claybarytes. The particles used for the suspension frequently are not available at the mine or plant where the suspension is to be used and sometimes they must be obtained from quite distant points so that their shipment involves considerable expense.

An object of the present invention is to enable use of the refuse of separating apparatus as the suspension particles. For example, by the present invention, the slime tailings of a froth-flotation separator may be used as the suspension particles.

Referring in more detail to the advantages obtained by use of the slime tailings of a froth-flotation separator as suspension particles, it will be appreciated that most plants for separating ores or raw coal include froth-flotation separators. For example, most large coal mines include large washeries divided among several buildings erected at various times. For example, a coal mine may have begun operation to exploit a high quality coal seam so that washing was not required. Later on, a washery may have been built, first a simple washery which, by later additions, became more complicated. Thus, while the mine eventually still may have'a single coal washing plant, the plant has become sub-divided into several units, each of which is in itself a large washery. The raw coal will be screened near the mining shaft, the nut sizes probably will be washed near the screens, while the fines resulting from the screening will be taken to one of the units to be separated by froth-flotation. In any event, the mine washery includes a froth-flotation separator, and a purpose of the present invention is to use the slime tailings from such a separator for the suspension medium in the sink-and-float process forming part of the Washing lant.

p Other objects and advantages of the invention will be apparent from the following specification and accompanying drawing wherein,

Figure l is an axial section of a hydrocyclone such as may be used in the process of the invention, and

Figure 2 diagrammatically shows the procedure of the invention as applied to treatment of raw coal.

In the preparation of a suspension in accordance with the invention, use is made of a hydrocyclone such as shown in Figure l. Hydrocyclone 10 includes a shallow top cylindrical portion 11 including a base plate 12 having an axial opening 13. An infeed supply pipe 14 opens tangentially to the portion 11. Beneath and concentric with portion 11 is a co-axial conical portion 15 provided with an axial apex opening 16.

Hydrocyclones of the above type heretofore have been used in the thickening of suspensions. Maximiliaan G. Driessen et a1. Patent No. 2,543,689, issued February 27, 1951, for Process for the Separation of Solids of Different Specific Gravity and Grain Size, the application for which 2,693,878 Patented Nov. 9, 1954 was filed of even date with the above identified original application, discloses use of such a hydrocyclone for the separation according to specific gravity of particles of difierent grain size and different specific gravity if there is added to a suspension of such particles a quantity of relatively fine particles of high specific gravity. In the absence of such relatively fine particles, the larger particles of the lighter constituents in a water suspension will leave the apex opening of the hydrocyclone with the particles of high specific gravity, a condition which cannot be tolerated in practical operation.

We have discovered that when a suspension of the slime tailings of a froth-flotation apparatus or similar separator is supplied under pressure to a hydrocyclone, perhaps with previous addition of water, the hydrocyclone not only separates the infeed according to specific gravity but also discharges the undesired very fine particles with the light fraction at the base aperture 13 of the hydrocyclone and discharges the heavier fraction, minus the undesired fine particles, through the apex opening 16.

' This is accomplished without the above-mentioned addition of relatively fine particles of high specific gravity because the slime tailings or other refuse already contain a high percentage of fine particles of relatively high specific gravity. Thus, in accordance with the invention, the apex discharge comprises a fraction of relatively high ash content and formed of particles Within the desired size limits. Furthermore, no screening is necessary to eliminate the undesired fine particles, the ash content and size range factors being determined in a single pass through the hydrocyclone.

Figure 2 diagrammatically illustrates the application of the present invention to a coal washing plant. As is indicated in the upper portion of Figure 2, a mixture of raw coal and water is delivered to a screen or other classifier 20. For example, the raw coal may be delivered at the rate of two hundred tons per hour, and if a screen of thirty-two mesh is used, forty tons of screenings comprising fine particles will leave the apparatus 20 by the line 21. The larger particle will leave apparatus 20 by the line 22 to move to the sink-and-float bath 23. With the above rate of infeed, one hundred sixty tons of material per hour will move through the line 22.

The material moving through line 21 will be delivered to the froth-flotation apparatus 24 which will separate the infeed into thirty-two tons of coal per hour which outfeeds through the line 25 while eight tons per hour of waste fines or slime tailings move through the line 26.

The line 26 may be provided with a flow divider to enable some of the flow therethrough to be discharged to waste by a line 27. In any event, such portion of the slime tailings as desired will be moved past the flow divider to a pump 28 which delivers its output at a pressure of the order of twenty-five pounds per square inch through the infeed line 14 to cyclone or hydrocyclone separator 10. Hydrocyclone 10 may have a maximum diameter of fourteen inches, an overall height of twenty inches and an apex opening one-half inch in diameter. As is indicated by the dotted line 29, water may be added to the hydrocyclone infeed between the flow divider and pump 28.

With hydrocyclone 10 operating in accordance with the principles mentioned above and described in said Driessen et a1. patent fine light particles will be discharged from the base opening 13 of hydrocyclone 10 and may move through line 30 to waste. The fine heavy particles will be discharged from the apex opening 16 to move by a line 31 for the purpose hereinafter described. The outputs of hydrocyclone 10 are subsequently described.

Referring again to the one hundred sixty tons per hour of coarse particles moving through the line 22 to sink and-float bath 23, these will be separated by the action of the suspension in the bath, which suspension may have a specific gravity of 1.55. In accordance with usual practice, the coal particles will be moved from the upper portion of one end of the bath and on to a screen 32 3; a secondhead 36 associated therewith, this head receiving Water from' a source hereinafter described: Gom partments 37 and 38 are provided below the respective screens 32 and 33, and the Water and fine particles fallihg. through; the screens: will move. from these: compart ments; byliires; 39' and: ill-to a pump 411 which; delivers the mixture; of fine particles; and water, by a line. 42 to. a. hydrocyclone; 43' of: the thickener: type: The; coal mov-- ing ofi the-screen'32: willlbe collected. and the wasterrnovfrom thescreen33smay be; discarded;

With the process.- described above; the-washings obtained in-thecornpartments 37 and 38 :obviously will be dilutedisuspensionwith a specifiegravity of: the order. of: 1.1; If thersuspension inthe bath 25:isto-be-maintained2 at 1.55, this diluted suspensionarnust. be thickened-to. that. specific gravity before it; is returned: tobath, 23. The fact. thatthe coal: and waste moving from.-the screens; 32 and 331r still. will: have; some suspension: particles adheringthereto-will. result ina'. loss ofithirty-five. hundred poundsoff weighting. or suspension. materialper hour. In other words, if. this. sprayedofi. suspension; is. notreplaced; new suspension: must be. added; regularly tothe. bath. 23. The: waste-fines or: slime tailingsmoving through line 26 can-- not be. directly used-for that purposeas they contain. only about 60% of. ash, and. approximately 50% by weight of this-is smaller than. 5'0 microns-r.

In order to replace theabove-mentioned thirty-five hundred pounds per 'hour' of weighting. material, five. tons per; hour of; the: slime tailings can be. pumped; into the hydroeyclone separator This will-result in discharge fromthe apex 16-of thirty-five hundred poundsofsolids per hour. with an. average ash content of 8.0%, 78% by weight of. this being of asizev greater. than. 50 microns but. naturally smaller than. the mesh of. screen. 20.. Because line 31 leading from the.apex.l.6 of hydrocyclone. 10 is connected. to line. 3.9;.the apexdischarge may. move through the:pump 41. to the hydrocyclonethickener 43 which. will be operated: to. produce an apex discharge. having the. required specific. gravity of 1.55. This. apexv discharge willv move through. the line. 44. to the bath 23;.

The. base: discharge. of? thickener 43' will. be: primarily watgr and. may move by. lines: 451 and 46. to the spray hea $36;

The base. discharge.of.separatinghydrocyclone 10, con? sisting of" Water, light particles. and very fine particles may be.dischargedthroughline 30..

If all of' the material. movingtlirough. the. line. 39 to. pump 41 is not. required, a.valve. 41 may be. suitably operated to dischargesomeoffitto waste. through aline.

it. wilt be observed that the. invention results. in the.

attainment of the objects stated above in that it permits lost suspension particles" tobe" replaced by particles obtained from the raw coal itself and by use of the usually convenient froth-flotation apparatus. Thus, no foreign weighting material has to.- be. used in the suspension. Moreover, the plant is quite simple, requiring but one specific'gravity' regulatorfor the bath, namely, the thickener 43.

It will be apparent that the process is applicable to material other thanraw coal;

The. terminology used: in the specificatiorris' for. the purpose'ofdescription and. not of limitation, the. scope of the invention'beingdefi'ned inzthe: claims.

We claim:

1. The method of separating raw coal according to a predetermined specific gravity comprising the steps of removing fines from the raw cOaL Subjecting the remaining raw coal to sink-and-fioat' separation in a suspension bath. of. said. predetermined specific gravity and. formed by fine. particles. and liquid,v subjecting the. fines: removed. fromlhe raw coal to froth flotation toseparate. the. same. into fine coal and waste, treating the waste so obtained. by hydrocyclone separation to remove therefrom very fine particles and particles of a specific gravityv lower than thatrequired to maintain the sink-and-fioat bath at said predeterminedspecific gravity, and delivering the. remaining fraction of said waste. to the sink-and-fioat sus-- pension bath to replace losses, therefrom.

2. The method of claim 1, wherein the coal andv shale. removed from the suspension bath is washed, said remainingfractionof treated Waste. is mixed'withsaid washings, theresultant. mixture. is thickened to obtain a frac tion of saidpredetermined specificgravity, and said. thickened'. fraction is then. delivered. to the. suspension bath.

References Cited in the file of this patent UNITED- STATES. PATENTS Number. Name. Date 13656271? Downs et al J'an.. 17,1928? 356,648 Brusset Aug. 22, 1944 2,543,689. Driessenvet a1 Feb. 27, 19,5'1'

EQREIGN PATENTS:

Number Country Date 8553.77 France May-9, 1940*- QTHER REFERENCES Journal. of. the. Institute of Fuel; vol. Xlh August 1939,. pp. 327-348. (Copy in Scientific Library.) 

